Device and method for truing a machining wheel by means of a rotating truing tool as well as machine tool with a device of this kind

ABSTRACT

The invention relates to a device ( 10 ) for truing a machining wheel ( 20 ), in particular grinding or eroding wheel, by means of a rotating truing tool ( 30 ), comprising:
         a first rotating spindle ( 18 ), which can be driven so as to rotate about a first axis of rotation ( 22 ), for attaching the machining wheel ( 20 ) and   a second rotating spindle ( 28 ), which can be driven so as to rotate about a second axis of rotation ( 32 ), for attaching the truing tool ( 30 ),   wherein, in order to true the machining wheel ( 20 ), the truing tool ( 30 ) rotatably driven by the second rotating spindle ( 28 ) can be brought into material-removing contact with the machining wheel ( 20 ) rotatably driven by the first rotating spindle ( 18 ). In this respect, in order to obtain uniform truing results, the first axis of rotation ( 22 ) is directed substantially orthogonally to the second axis of rotation ( 32 ) during the entire truing process.

The present invention relates to a device for truing a machining wheel, in particular grinding or eroding wheel, by means of a rotating truing tool, comprising:

-   -   a first rotating spindle, which can be driven so as to rotate         about a first axis of rotation, for attaching the machining         wheel and     -   a second rotating spindle, which can be driven so as to rotate         about a second axis of rotation, for attaching the truing tool,

wherein, in order to true the machining wheel, the truing tool rotatably driven by the second rotating spindle can be brought into material-removing contact with the machining wheel rotatably driven by the first rotating spindle.

The present invention also relates to a corresponding method as well as a machine tool which is equipped with a device of this kind.

Wear regularly occurs when grinding and eroding workpieces by means of rotationally symmetrical machining wheels, such as grinding wheels or eroding wheels. Although modern machine tools have wear compensation programs which enable this wear to be compensated within certain limits, machining wheels of this kind have to be trued at regular intervals. The machining wheel then regains the dimensional and geometrical accuracy which is lost in the grinding or eroding process as well as the sharpness. It is only possible to achieve machining results which are also of a high precision with regularly trued machining wheels.

Therefore modern machine tools, in particular machining centres, as a rule have an integrated truing device in order to true the machining wheels which are used from time to time. There are basically two possibilities for this, that is truing with stationary and moving truing tools. Moving truing tools are in most cases used in modern machine tools in order to keep the wear on the truing tool to a minimum and in order to lengthen its service life. In this case, in order to true a machining wheel, both the truing tool and the machining wheel are rotatably driven and brought into material-removing contact with one another.

In this connection the machining wheel and the wheel-like truing tool were as a rule set obliquely to one another in the prior art, so that the first axis of rotation associated with the machining wheel was disposed at an acute angle to the second axis of rotation associated with the truing tool. However this resulted in punctual contact between the machining wheel and the wheel-like truing tool, which led to shape-changing abrasion on the truing tool. Consequently rigidly predetermined contours of the machining wheel could only be obtained to an unsatisfactory degree by means of the truing tool, which was irregularly abraded in terms of its shape. On account of the oblique orientation of the two axes of rotation relative to one another, it also became difficult to accurately predict the irregular abrasion on the truing tool and to compensate for this by means of an appropriate compensation program. It was therefore necessary to take additional precautionary measures, such as, for instance, an optical monitoring system, in order to accordingly detect wear occurring on the truing tool and to adjust this accordingly.

As an alternative to the oblique arrangement of the two axes of rotation of the machining wheel and the truing tool relative to one another, it is known from DE 34 28 426, for example, to orient the axes of rotation of the machining wheel and the truing tool substantially parallel to one another. Even through improved truing results could thereby be obtained, the disadvantages described above continued to exist, as quite different abrasion phenomena frequently arose over the circumference of the rotating truing tool, and these then appeared in an undesirable manner on the profile to be trued of the machining wheel.

DE 34 37 682 C2 presents a device for truing double-cone grinding bodies in which the axis of rotation of the spindle is disposed perpendicularly to the axis of rotation of the double-cone grinding body, and replaceable truing heads are attached to the spindle by a fastening element.

DE 1 289 449 discloses a truing device for grinding wheels in which the axis of rotation of a shaft which bears the truing roll is disposed substantially perpendicularly to the axis of rotation of the grinding wheel which is to be trued. The truing roll is guided around the corners and over the surface of the grinding wheel by a template and a sensing roll, which has the same diameter as the truing roll.

In contrast to this, an object of the present invention is to provide a device as well as a method of the type initially described with which the truing result can be improved at a low technical expense.

This object is achieved by a device of the type initially described in which the first and the second axis of rotation do not intersect during the entire truing process, and the first axis of rotation is oriented substantially orthogonally to the second axis of rotation during the entire truing process such that the truing tool wears uniformly over its entire circumference during the entire truing process.

The applicants have recognised that wear phenomena on the truing tools can be better controlled through a substantially orthogonal arrangement of the first axis of rotation, associated with the machining wheel, relative to the second axis of rotation, associated with the truing tool, these axes not intersecting during truing. In connection with the invention “substantially orthogonal” means that a deviation from the entirely orthogonal orientation by +/−10° is possible. In other words, in spite of the wear occurring on the truing tool, a truing result which is substantially independent of this can be achieved through an axial orientation of this kind.

The contacting point between the truing tool and the machining wheel is, according to this axial arrangement, located on the outer diameter, i.e. on the “equator” of the respective wheel. Due to the axial arrangement according to the invention, the truing tool wears substantially uniformly over its entire circumference, so that no wear-induced profiles which have a negative influence on the truing result are produced on the truing tool. It is understood that it is possible to move both the truing tool relative to the machining wheel and the machining wheel relative to the truing tool when truing. According to one constructional variant of the invention, the second rotating spindle can be displaceable relative to the first rotating spindle during truing, with the second axis of rotation associated with the second rotating spindle being movable along a path extending parallel to a desired profile of the machining wheel. In this connection the truing tool can be movable along a linear path extending parallel to the second axis of rotation in order to true the machining wheel. This constructional variant is a possibility when, for example, the machining tool has substantially plane surfaces. It is also conceivable in this respect for the truing tool to act with a circumferential surface on a front side of the machining wheel. This is particularly a possibility when a cup wheel is to be trued, i.e. when, given a cup-like machining wheel, its front face which is orthogonal to the axial direction is trued with the truing tool. The rotating truing tool then moves orthogonally to the first axis of rotation, about which the cup wheel rotates, and therefore acts on the front face so as to remove material.

According to one constructional variant, the truing tool can act with a circumferential surface on a circumferential surface of the machining wheel. This truing variant is in particular used when a machining wheel is trued at its circumferential surface, the circumferential surface being substantially of circular cylindrical form ation.

According to the invention, in order to true a profiled machining wheel, i.e. one which is not of entirely circular cylindrical formation, at its circumferential surface, it is also possible, in order to true the machining wheel, for the truing tool to be movable along a curved path which extends parallel in direction to a curved contour to be trued of the truing tool. This means that the truing tool is displaced in direction components both parallel and orthogonal to the first axis of rotation, with the second axis of rotation describing a path which extends substantially parallel in direction to the desired profile of the machining wheel.

It is also possible according to the invention for the second rotating spindle to be approachable to the first rotating spindle in order to compensate for material removal at the machining wheel or/and at the truing tool caused by the truing, with the spacing of the first and second axis of rotation decreasing. It is as a result possible to compensate for wear on the truing tool, although also on the machining wheel. Truing wheels frequently consist of SiC (silicon carbide), corundum or special fused alumina. However it is also possible to use a truing tool of a diamond grit material, in the case of which the amount of material removed is relatively small. Wear can be detected at the truing wheel through active measurement with a measuring probe or without contact, for example optically or through structure-borne sound measurement.

As already indicated above, the invention also relates to a method for truing a machining wheel, in particular a grinding or an eroding wheel, by means of a rotating truing tool with a device of the type described above, wherein, in order to true the machining wheel, the truing tool rotatably driven by the second rotating spindle is brought into material-removing contact with the machining wheel rotatably driven by the first rotating spindle, wherein the first axis of rotation is maintained substantially orthogonal to the second axis of rotation. According to the above description with regard to the device, it is also possible with regard to the method according to the invention for the second rotating spindle to be displaced relative to the first rotating spindle during truing such that the second axis of rotation associated with the second rotating spindle is moved along a path extending parallel to a desired profile of the machining wheel.

Furthermore, it is likewise possible with the method according to the invention for the truing tool to be moved along a linear path extending parallel to the second axis of rotation in order to true the machining wheel. As an alternative to this, the method according to the invention can also provide, in order to true the machining wheel, for the truing tool to be moved along a curved path which extends parallel in direction to a curved contour to be trued of the truing tool. As already indicated above, in order to achieve the relative movements between the truing tool and the machining wheel, one of these components can in each case be maintained stationary, with the other component executing the required relative movements. As an alternative to this, however, it is also possible to simultaneously move both components, truing tool and machining wheel, for example such that the truing tool executes movements in one plane and the machining wheel executes a movement in a direction orthogonal to this plane (third axis).

It is also possible with the method according to the invention for the second rotating spindle to be approached to the first rotating spindle in order to compensate for material removal at the machining wheel or/and at the truing tool caused by the truing, with the spacing of the first and second axis of rotation decreasing.

Finally, the invention also relates to a machine tool, in particular grinding or/and eroding machines, with a device of the type described above, wherein the first axis of rotation is formed by a machining spindle holding the machining wheel, and wherein the second rotating spindle is formed by a truing spindle which can be displaced relative to this.

The invention is illustrated in the following by way of example in the light of the accompanying figures, in which:

FIG. 1 is a perspective representation of a machining spindle and a workpiece holding device with a truing spindle attached thereto;

FIG. 2 is a schematic representation showing a profiled machining wheel being trued;

FIG. 3 is a schematic representation showing a cup wheel being trued according to the invention;

FIG. 4 is a representation according to FIG. 3 showing a circular cylindrical circumferential wheel being trued according to the invention; and

FIG. 5 is a schematic representation showing a profiled circumferential wheel being trued according to the invention.

A detail of a machine tool according to the invention is represented and generally marked by 10 in FIG. 1. This has a machining head 12 which is fastened in a machine frame in a manner which is not shown. The machine tool also has a workpiece holder 14, which is likewise attached to the machine frame in a manner which is not shown.

At its lower end the machining head 12 has a machining spindle 16 with a spindle shaft 18, to which a machining wheel 20 is attached in a rotationally rigid manner. The spindle shaft 18 can be driven so as to rotate about an axis of rotation 22 for rotatably driving the machining wheel 20. The machining wheel 20 is a grinding wheel, although it can equally be formed as an eroding wheel.

A workpiece accommodating device 24 is provided on the workpiece holder 14. Attached to the side of the workpiece accommodating device 24 is a truing spindle 26, on the rotatably drivable spindle pin 28 of which a truing wheel 30 is mounted in a rotationally rigid manner. The truing wheel 30 can be driven so as to rotate about a second axis of rotation 32. The axes of rotation 22 and 32 extend substantially orthogonally to one another, that is during the entire truing process.

FIG. 2 is additionally to be considered for a more detailed illustration of the truing operation. Here the truing wheel is shown in three different positions 30 ₁, 30 ₂ and 30 ₃, with the positions 30 ₁ and 30 ₃ showing the end points of the truing machining and the position 30 ₂ showing a central position. During truing the axis of rotation 32 of the truing wheel 30 (see FIG. 1) extends along a path 34 which is substantially parallel in direction to the outer contour 36 of the machining wheel 20 which is to be trued. This outer contour is substantially in the shape of a circular segment in the cross section which is shown in FIG. 2.

Due to the orthogonal orientation of the axes 20 and 32, regular wear occurs at the circumference of the truing wheel 30 when truing, so that no punctual irregularities can occur at the outer profile 36 when simultaneously rotating the machining wheel 20 to be trued and the truing wheel 30. By repeatedly departing from the path 34 by means of the truing wheel 30 in an opposite direction in each case with small feed movements of the truing wheel 30 relative to the wheel 20, thereby compensating for wear on both wheels induced by truing, an optimal, regular truing result at the machining wheel 20 is obtained in spite of the fact that material is removed at the truing wheel 30 and, to a small degree, also at the wheel 20 which is to be trued.

FIGS. 3 to 5 show different truing situations according to the invention. It is understood that here the machining situation is shown in a side view of the machining wheel 20 on the left-hand side and in a front view of the machining wheel 20 on the right-hand side.

FIG. 3 shows a cup-shaped machining wheel 20 which is machined with the truing wheel 30 at its front-side surface 38. Here the truing wheel 30 rotating about the axis of rotation 32, which is orthogonal to the plane of the drawing in the left-hand part of the figure, is in material-removing contact with the surface 38. It is displaced to-and-fro along its axis of rotation 32 according to the arrow P transversely to the machining wheel 20, with the machining wheel 20 rotating about its axis of rotation 22.

FIG. 4 shows a second machining situation in which the circular cylindrical circumferential surface 40 of the machining wheel 20 is trued with the truing wheel 30. The axes of rotation 22 and 32 are again orthogonal to one another. The truing wheel 30 rotating about the axis of rotation 32 is moved to-and-fro according to the arrow Q in material-removing contact with the machining wheel 20 parallel to the axis of rotation 22 thereof, with the machining wheel 20 also rotating. The movement along the arrow Q is a linear movement corresponding to the cylindrical outer contour 40 of the machining wheel 20.

The situation in the embodiment according to FIG. 5 appears differently. In this situation the outer contour 42 of the machining wheel 20 is in the shape of a circular segment in cross section. A movement of the truing wheel 30 along the arrow R is accordingly also superimposed on the movement of the truing wheel 30 along the arrow Q, so that the overall result is a movement of the axis of rotation 32 along a circular path, as is shown in FIG. 2, for instance. 

1. Device (10) for truing a machining wheel (20) by means of a rotating truing tool (30), comprising: a first rotating spindle (18), which can be driven so as to rotate about a first axis of rotation (22), for attaching the machining wheel (20) and a second rotating spindle (28), which can be driven so as to rotate about a second axis of rotation (32), for attaching the truing tool (30), wherein, in order to true the machining wheel (20), the truing tool (30) rotatably driven by the second rotating spindle (28) can be brought into material-removing contact with the machining wheel (20) rotatably driven by the first rotating spindle (18), characterised in that the first and the second axis of rotation do not intersect during the entire truing process, and that the first axis of rotation (22) is oriented substantially orthogonally to the second axis of rotation (32) during the entire truing process such that the truing tool wears uniformly over its entire circumference during the entire truing process.
 2. Device (10) according to claim 1, characterised in that the second rotating spindle (28) can be displaced relative to the first rotating spindle (18) during truing, wherein the second axis of rotation (32) associated with the second rotating spindle (28) can be moved along a path (34) extending parallel to a desired profile of the machining wheel (20).
 3. Device (10) according to claim 2, characterised in that the truing tool (30) can be moved along a linear path extending parallel to the second axis of rotation (32) in order to true the machining wheel (20).
 4. Device (10) according to claim 3, characterised in that the truing tool (30) acts with a circumferential surface on a circumferential surface (40) of the machining wheel (20).
 5. Device (10) according to claim 2, characterised in that, in order to true the machining wheel (30), the truing tool (30) can be moved along a curved path (34) which extends parallel in direction to a curved contour (42) to be trued of the machining wheel (30).
 6. Device (10) according to claim 1, characterised in that the second rotating spindle (28) can be approached to the first rotating spindle (18) in order to compensate for material removal at the machining wheel (20) or/and at the truing tool (30) caused by the truing, wherein the spacing of the first and second axis of rotation (22, 32) decreases.
 7. Device according to claim 1, characterised in that the machining wheel is a grinding or an eroding wheel.
 8. Method for truing a machining wheel by means of a rotating truing tool, with a device according to claim 1, wherein, in order to true the machining wheel, the truing tool rotatably driven by the second rotating spindle is brought into material-removing contact with the machining wheel rotatably driven by the first rotating spindie, wherein the first and the second axis of rotation do not intersect during truing and the first axis of rotation is maintained substantially orthogonal to the second axis of rotation during the entire truing process such that the truing tool wears uniformly over its entire circumference during the entire truing process.
 9. Method according to claim 8, characterised in that the second rotating spindle is displaced relative to the first rotating spindle during truing such that the second axis of rotation associated with the second rotating spindle is moved along a path extending parallel to a desired profile of the machining wheel.
 10. Method according to claim 9, characterised in that the truing tool is moved along a linear path extending parallel to the second axis of rotation in order to true the machining wheel.
 11. Method according to claim 9, characterised in that, in order to true the machining wheel, the truing tool is moved relative to the machining wheel along a curved path which extends parallel in direction to a curved contour to be trued of the machining wheel.
 12. Method according to claims 8, characterised in that the second rotating spindle is approached to the first rotating spindle in order to compensate for material removal at the machining wheel or/and at the truing tool caused by the truing, wherein the spacing of the first and second axis of rotation decreases.
 13. Machine tool, in particular grinding or/and eroding machine, with a device (10) according to claim 1, wherein the first axis of rotation (22) is formed by a machining spindle holding the machining wheel (20), and wherein the second rotating spindle (28) is formed by a truing spindle which can be displaced relative to this. 